The present invention relates generally to magnetic resonance imaging (MRI) and intracavity probes used in MRI, and, more particularly, to MRI probes for MRI guided biopsy and delivery of therapy of the prostate.
Prostate cancer is the second leading cause of cancer death among men. Due to the non-specificity of prostate specific antigen (PSA) screening, in which a high level of PSA signifies a possible tumor problem but is also associated with benign prostate hyperplasia and prostatitis, many biopsy procedures must be undertaken to confirm a diagnosis in accordance with high PSA levels. In particular, no surgical or radiation therapy can proceed without a positive biopsy result.
Ultrasound imaging does not visualize lesions very well in the prostate and, as a result, the biopsy procedures are taken in a random fashion over the several sectors of the prostate. The ultrasound imaging is used to locate the prostate and guide the biopsy needles to specific locations in the sampling pattern, which may involve up to 6 or 8 biopsy samples. A positive biopsy finding would prompt further treatment or therapy, under current medical procedures. However, a negative biopsy does not necessarily mean the patient is free of cancer, since the sampling procedures may not find suspect tissue.
Ultrasound guided biopsy of the prostate is a common procedure. The ultrasound is used to image the prostate in real time. Because of a fixed geometry between the ultrasound crystal and the needle guide, it is possible to project the location of the biopsy volume directly on the image screen as the probe is moved and manipulated. Ultrasound guided biopsy probes are cylindrical in shape and not larger in diameter than 2.5 cm. This diameter is at the limit of acceptability to some 95% of patients . . . for the other 5% the probe diameter is too large and there is sufficient discomfort for the procedure to be stopped. Such a probe design is possible for MR applications but is not optimal for coil placement close to the rectum.
MR imaging with an internal surface coil, the endorectal coil, which is inserted into the rectum, gives very good images of the prostate and of the cancer lesions. MR imaging provides the ability for accurate and real-time localization of suspected lesions. Thus, acquiring images by MR imaging for guiding biopsy needles would reduce the number of biopsy samples, and the random sampling procedure could be eliminated given the ability to localize suspected lesions.
A current probe design for acquiring MR images is the commercially available endorectal coil for MR, which is a flexible coil that is expanded inside the rectum by a balloon. However, it is not suitable for delivery of biopsy needles or of therapy devices as there is no firm base from which to reference position of the interventional devices.
For MR guided prostate biopsy or prostate therapy, a number of requirements need to be met which are unique to the combination of MR detection and the capabilities of therapy and/or biopsy devices in one probe. In order to obtain high resolution MR images, it is desirable that a receive coil is incorporated into the probe and that this coil be placed as close as possible to the prostate. The coil location is desirably in close proximity to the rectum because the signal sensitivity of a small receive coil falls off sharply with distance. By necessity, for purposes of patient comfort, the receive coil width is desirably no larger than about 2.5 cm. Another requirement is that the device be easily manipulated inside the rectum to be able to sample the entire prostate for biopsy purposes or for the application of therapy. Thus, all sectors of the prostate are desirably accessible. The device is desirably substantially rigid to provide a firm base for biopsy needle guides or for ultrasound crystals. The device is desirably of sufficient size to physically incorporate the needle guides or crystals. Finally to locate the image plane precisely and follow it as the probe is moved or as the patient moves, a set of Magnetic Resonance (MR) tracking coils are incorporated as well. These requirements pose a challenge for the design of an appropriate probe.
What is needed is a probe configuration for MR imaging an intracavity region of interest proximal to the cavity, such as the prostate. Further needed is a probe configuration that allows access to all areas of the prostate for biopsy sampling or for the introduction of therapeutic devices during MR image acquisition, in order to accurately and in real-time localize suspected tissue of the region of interest.
An insertable intracavity probe for use in Magnetic Resonance Imaging (MRI) and therapy of a region of interest proximal to a cavity is provided. The probe comprises, a substantially rigid probe shell for insertion into the cavity. The probe shell is adapted to incorporate at least one device for imaging the region of interest, and the probe shell further being adapted to incorporate at least one therapy device, such as a biopsy device or therapy delivery device, for application on the region of interest during imaging. Further, a method for MRI guided biopsy and therapy delivery to a region of interest proximal to a cavity is provided.